Single-element distance ground relay



g- 15, 1949- s. 1.. GOLDSBOROUGH ,3 5

SINGLE-ELEMENT DISTANCE GROUND-RELAY Filed April 29, 1948 WITNESSES: iNVENTOR Shir/e L, Goldsborou 12. %%Z% 5 9 ATTORNEY Patented Aug. 16, 1949 UNITED *i'STAT'E-S *oFFI-eE 2,479345 f. SINGLE-ELEMENT DISTANGKGROUND RELAY Shirley L. Goldsborough;'Baslgin'gRidge; N. J., assignor to Westinghouse-"E1ectric Corporation,

East Pittsburgh, Pa., a corporat-ion ofPennsylvama ApplicationApril 29, 1948, Serial Noi24,040

' 3 "Claims. (GI; "17 5- 294) 7 1 2 "'Myinventiofi relates to a ground reactance shown nthat the smallestmodified'voltage is still relay which is'as'so'cia'tedwith networks for mak- (the voltage ot the faulted;phase;(For the mini- -"ing' the proper phase selection in the event of 7niuin voitagefr etworks,'ILprefera type shown in a single ground fault one three-phaseline which my jeop'nding,japplication fierial No; 788,583, filed is being protected. NQvembe'rjZS; l.l9ii7',1 ;us ingfre'qtifiers, so that my i It has been known, 'sinc'ethe' publication of the j;lsingle elerneht'groundg'reactance relayhas direct- L'Lewis Patent"1 ,'897,()22 1111933; that a reactance currenteriergizefion, I f relay can be used for fairly accurately measuring *iiWith the foregoing and'otherobjects in view, the' distance of ground-faults, irrespective of the nsists of "the circuits, systems, "ground faultresistance, if the relay-current or p H apparatus parts and methods of Zfthe relay 'v'olta'geis properly compensated forlthe "design'andoperationjdescljibfiiland claimed in effects of various phase-sequence components of r .the following. specificatio'ri and illustrated in the 'f'th'e' currents in the-faulted line and in any parm'laceornpanying djr'awingythfi.$1nglefigure of which ""allel line or lines. Z'isj'a 'simplified diagrammatic view of eircuitsand A suitable form of. high-speed beam-type rel5iabparatusw emhodyingmy.invention in an illus- -a"ct: rnce'-'.relav is .shown' in Fig. 3 of the Lewis .ltrative forrn iemb'gdiment.

'Patent"1',967j093 of 1934, and animpro'vedform I 'haveillustrat ,j my invention asbeing apo'f-f 'this 'relay. is shown in the Mehring Patent .,p1ie d tothe 'proteetion offajline-section 1, which 2,439,944," granted April 20, 1948, on an application .Lrn'ay belfa part of ;a: three-phase, 60ecycle trans- Serial No."'576,9'73. In this improved reactancerhissioh or,di'st'rihution"system. The three-phase 'rela'y, a"beam-type relay or other'difierential reline isjconneict'e j three-phasebus z through "1a;y -i's provided with a restra'inihgiorce 'respon- L'liineesegregaltingicntcu teinterrnpting meanssuch sive to the" line-voltage, and an operating force as qathree phasejcircuit breaker 3, whiohisillus- V ""res'pofnsiveto the vectorial sum oflthe same volt- \"t 1"ated a's haying an auxil aliy;make;contact 3a age" plus the line-current lagged 90, this cur- ;.and a tripj, Oil'j TCi In theflgeneralvcase there Trent-responsive current-component being introare, also one orgmorjefl paralletlines ,4 paralleling dficd by means of an' air-gap current-transjfgthegprdteotsd.line-section asgshown in the 'foimer- Which is used as a mixing-transformer or drawing. 7 H J g I V Tfeo'inpensat'or reactor. 'The,,threej-,phase. relaying currentsfland volt- In194,6,my'Patent"2,408,208was granted,.showages are aemedimm'me protected line-section "mgthe use of phase-selector-operatedi switch- 'cj by means oiling-current .tr n formersi and ing m'eans for switching the proper voltageonto ilqtjentiahtransjormers ,GLgJQ PeQtiveIy, for re- "a single ground reactan'ce relay, sothat'asingle spending to; the line rent, and to the line- 'relaywouldrespondtogroundefaults on any one .fvoltage; ,Ajpan}; of a Xiliary,potentialrtransof the three phases of the protected line. 5 formers T mayalslobe'. 6.1 6 i, d ,from the potenf An object of my present inventionis to protial -transfqrmersiifi fQr'. p'rpvidin a response to vide fninimumvolta'ge networks, in place ofthe tlie\.z'eiiosequence'voltage component. The parselector-operated switching-means, forenergiz- "iallel liri 1.5 is. a 0,.D'1".Qvided..W th l n -C n? iiigboth the operating side and the restraining transiorme'rs 8. v side 'ofar'eactan'ce r'elay of the type shown in iyflienthe relayingleq uipm ntlis.usedona powthe Mehrihg'patent; otherwiseusing the c'onnec- ,.e11"-Jsy's e1@r1,whioh is grounded atsmorelthans one tions shown'in rnvi ifi'patent." Ontherestraintfjpoi nifl, or fwhichi otherwise involves errors in side,-I-1 1se the smallest of the suitably' compen- "'ground fatil't distances-me ment due to the fsated line-to-neu'tral voltages,andrthis-sniallest anannerinwhiqh thepo itwfi. nega fi d "voltage is'obvio usl y the voltage of thelifaulted -;sequ'enQe il j.n.t.S.d tibute themselvesjtis necphase, in the event of a single grouridl faultg On "essa'ry fton'seQsorn sort of compensating means the 'operatingside luse the same compensated I ;.as' setiiforthliri the ,Lewi atentQlfiQ'LOZZ In voltage,to'which is added aiagg'ed zero-sequence 1 order ,jt p' vide, waI'groiin -dp,, ta,nce relay which current-'eoiiiponent biit this currentcomponent c i, any, diiferenttransdoes not needto be very large,"andanalysishas ms; 1' therefore use such compensation. As in the case of my Patent 2,408,208, I prefer the voltage-compensated method which is shown in Fig. 9 of said Lewis patent. I also prefer the reactance-relay of the Mehring patent, and the use of zero-sequence line-currents to measure the zero-sequence reactance to the point of location of the fault.

As shown in the drawing, the illustrated compensating method uses three compensators CA, CB and CC, one for each phase, and when there is a parallel line such as the line 4, another compensator CP, one for each of the parallel lines. The three phase-responsive compensators CA, CB and CC have auxiliary current-transformers 9 which are energized from the respective phasecurrents of the line, from which the zero-sequence component has been removed, and these auxiliary current-transformers '9 are used to energize suitable impedances I0, which are adjust-' In the case of current-transformer 9' energizes an adjustable impedance H3.

The zero-sequencecurrent-component is withdrawn from the relaying currents of the protected line-section l by means of a suitable grounding-transformer such as an interconnected-star bank If. The neutral point of the interconnected-star bank H is connected to the neutral point of the line-current transformer 5 through the current-coil l3 of a ground-directional element DO, and the adjustably tapped primary winding I4 of an air-gap current-transformer or mutual reactor iM.

The adjustable impedances ID of the three phase-responsive compensators CA, CB and CC are respectively connected in the three phaseto-ground voltage-circuits 2|, 22 and 23 which are energized from the respective phases A, B and C of the potential-transformers 6.

. In accordance with my present invention, the voltage-circuits 2 i, 22 and 23 are used to energize two minimum-voltage networks N and N. Each minimum-voltage network N and N derives three modified line-voltages Ea, Eb, E0, and Ea, Eb, Ec, respectively, which are obtained in the secondary windings of potential-transformers Ta, Tb, Tc and Ta, Tb, Tc, respectively. The primary windings of the transformers Ta, Tb and To have one terminal connected to the respective voltage-circuits 2|,, 22 and 23, while their other terminals are connected to a common neutral connection 24. The neutral connection 24 is connected, through the secondary Winding 25 of the mutual reactor giM, to another common neutral connection 2 which is connected to one terminal of the primary windings of the transformers Ta, Tb and Tc of the other network N. The other terminals of the primary windings of these transformers Ta, Tb and Tc are connected to the respective voltage-circuits 2|, 22 and 23. The second common neutral circuit 24' is connected to the adjustable impedance ID of the parallelline compensator CP, and thence to ground and back to the secondary windings of the line-voltage potential-transformers 6.

The six modified line-voltages Ea, Eb, Ec, Es, Eb and E0 of the two minimum-voltage networks N and N are each rectified by a separate rectifier-bridge 26, each bridge having its direct-current output-terminals shunted by its own resistor sR and (preferably also) by its own Cal ripple-smoothing capacitor 21. The positive output-terminals of the six bridges 26 are connected to a common positive bus q. The three negative output-terminals of the bridges 26 of one network N are separately connected, through individual rectifiers Ra, Rb and Re, to a common negative bus :1: for that network. The three negative output-terminals of the bridges 26 of the other network N are likewise separately connected, through individual rectifiers Rs, Rb and Re, to a common negative bus as for that network. The rectifiers Ra, Rb, Re, Ra, Rb and Re conduct current in the direction toward the respective negative buses in and x.

The two minimum-voltage networks N and N use a common direct-current source which is represented by positive and negative terminals and The positive terminal is connected to the common positive bus q of the two networks. The network N has an operating-coil 30 and a restraint-coil rR mounted on a common magnetic circuit 3!. In like mannor, the other network N has an operating-coil 3t and a restraint-coil rR' mounted on another common magnetic circuit 3 l The two restraintcoils TR and rR are energized between the negative terminal and the respective negative buses ac and 3:, each in its own minimum-voltage network. The two operating-coils 30 and 30 are both energized from the positive and negative buses and In accordance with my invention, the two magnetic circuits 3| of the two minimum-voltage like, I have shown it only as a means for protecting the protected line-section l against single line-to-ground faults, and comprising, in addition to the ground-distance element HG, a

ground-directional element DO. This grounddirectional element D0 is shown as a producttype relay having a current-coil i3 as previously described, and also having a voltage-coil33 which is energized, responsively to the residual line-voltage, from the auxiliary potential-transformers l. The ground-directional relay DO has ,a contact 34 which is used in a tripping circuit which extends from the negative terminal through the two relay-contacts 34 and 32, the trip-coil TC, and the auxiliary breaker-switch 3a, and thence to the positive terminal The operation of my invention is based upon the equation for the line-to-ground voltage EaG of the faulted phase at the relaying station, calling the faulted phase phase-A, and assuming a lineto-ground fault at a distance which is m times the length of the protected line-section.

I shall use the following notation:

I Ia-=zero-sequence cu in the protected line-section,-

Mo=zero--sequence 'mutua-l impedance between the protected--line-section and each of the otherparallelli-nes; l Io=zero-sequence current in the parallel line or Rr=iault-resistance,

Ir=total iault current from both ends of theprotected line-section,

m=fractional part-of 'thedength of the protected line-section from the relaying station to the fault,

n=fractional part of the length of the protected line-section from the relaying station to the balance point of the relay,

Er=voltage on the restraint-side of the relay,

0o=power-factor angle of the zero-sequence current I0 with respect to the zero-sequence linevoltage E0, and

X0=Z0 sin 0o=zero-sequence reactance of one conductor of the protected line-section.

The phase-A line-voltage at the relaying station, assuming a phase-A ground-fault, is

For the voltage applied to the restraint-side of my ground-reactance relay HG, I use the same modified line-voltage as in Fig. 9 of the Lewis Patent ,897,022, namely,

The operation of the minimum-voltage networks N and N is to select the smallest of the three input-voltages. Thus, if Ea is the smallest input-voltage in the first network N, the rectified Ea voltage will be the voltage across the resistor 5B which shunts the direct-current terminals of the bridge 26 in this circuit. Neglecting the drop in the rectifier Ra', the voltage of the coil TR, which is the voltage between the negative bus at and the negative terminal will be the difference between the voltage E of the direct-current source represented by the terminals and and the rectified Ea, voltage. Assuming that the rectifiers Rb and Re conduct no current in their non-conducting directions, and assuming that the rectified voltages Eb and E0 are both larger than the rectified Ea voltage, the phase-B and phase-C bridges can have no effect on the circuits of the network N. The coil 30 opposes the coil TR and cancels out the E part of the response of the coil TR, leaving only the response to the rectified Ea voltage. The other -network N similarly responds to its rnimnium voltage Ea. .3:

l r The minimum Ea :voltage of thersecond network N: is the voltagev Er of Equation 2; g:

The minimum Ea voltage iOf the first network N is the vectoriaksumof Er and ''=y'KMI,n, where K represents the transformationratio, asdeter- I mined by the tap-settingtof. the mutual} reactor -9'M. IngeneraLathe modifieddineevoltage Er; as

expressed in'Equ'ationxZ, can-be considered to be in phase with the line-voltage-Eae;..and1if this is not so; in anyparticularrtransmissionesystem, it

is generally feasible to readjust the line-impedances, particularly the neutral-grounding impedances, so that this will be so.

Hence, the minimum Ea voltage of the first network N is approximately equal to E,-KMI A (-0 At the balance-point of my ground-distance relay HG, the operating-force is equal to the restraint-force, or

It will be understood, of course, that the example which I have given is only illustrative. I could have used other phase-sequence compensations, other reactance-relays, or other minimumvoltage networks, although the illustrated example has considerable merit. I wish it to be understood, therefore, that my invention, in its broadest aspects, is subject to considerable modification, in the way of additions, omissions, and the substitution of equivalents, and I desire that the appended claims be given the broadest interpretation consistent with their language.

I claim as my invention:

1. A single-element relay for a polyphase line, said relay having two energizing-means for producing two relay-fluxes, two minimum-voltage networks for energizing the respective energizing-means of the relay, each of said networks having a plurality of input-circuits and a plurality of rectifier-means for energizing a common direct-current flux-producing means in accordance with the smallest of the input-voltages of that network, means for energizing the respective input-circuits of one of said networks in accordance with a plurality of voltages of the polyphase line, and means for energizing the respective input-circuits of the other network in accordance with the vectorial sums of a plurality of voltages of the polyphase line plus a voltage-component having an out-of-phase response to a current derived from said polyphase line, the current-response being sufiieiently small so that the vectorial sum for the faulted phase is in general the smallest of the plurality of vectorial sums.

2. The invention as defined in claim 1, characterized by said relay being a differential relay having an operating means and a restraining means, each responsive to the output of one of said networks, the operating means being responsive to the network which is responsive to the minimum vectorial sum of voltage and current, and the restraining means being responsive to the network which is responsive to the minimum voltage.

3. A single-element difierential relay having an operating means and a restraining means, two

minimum-voltage networks, each having a plu- T 'rality of input-circuits and a plurality of rectifier-means for energizing a common'bus with a direct-current voltage approximating the difierence between a given direct-current voltage E and the minimum rectified input-voltage of that net- Work, means for similarly energizing the operatgizes the restraining means of the relay in accordance with a plurality of voltages of the polyphase line, and means for energizing the respectiveinput circu'itsbf the other network' in accordance with the vectorial sums of the same set of voltages plus a voltage-component having an out-of-phase response to a current derived from said polyphase line, the current-response being sufficiently small so that the vectorial sum for the plurality of faulted phase is in general the smallest of the vectorial sums. SHIRLEY L. GOLDSBOROUGH.

No references cited. 

